Several years ago, a friend of mine was installing phone equipment in a new high rise office building. The chassis case got grounded to a metal member in the wall. As the AC power got plugged into a standard grounded outlet, the magic smoke was let out of the box and things got hectic. After unplugging, he started looking for the reason. Eventually he discovered a potential difference between the AC ground and the (supposedly) grounded building frame: 80V! More than enough voltage to toast an electrical circuit. I'm hazy at this point as to the fix, but I believe he installed some kind of isolation device, like a transformer.
I bet he wished he had a virtual ground that day!
kenjj